NEW YORK -- For three years federal agents trailed Mohammed Yousry, a chubby 50-year-old translator and U.S. citizen who worked for radical lawyer Lynne Stewart. Prosecutors wiretapped his phone, and FBI agents shadowed and interviewed him. They read his books and notepads and every file on his computer.

This was their conclusion:

"Yousry is not a practicing Muslim. He is not a fundamentalist," prosecutor Anthony Barkow acknowledged in his closing arguments to a jury in federal district court in Manhattan earlier this year. "Mohammed Yousry is not someone who supports or believes in the use of violence."

Still, the prosecutor persuaded the jury to convict Yousry of supporting terrorism. Yousry now awaits sentencing in March, when he could face 20 years in prison for translating a letter from imprisoned Muslim cleric Omar Abdel Rahman to Rahman's lawyer in Egypt.

In June 2000, Stewart released to a reporter a version of the letter, which discussed a cease-fire between Islamic militants and the Egyptian government. Prosecutors said that the lawyer and the translator, by these acts, conspired to use Rahman's words to incite others to carry out kidnappings and killings. No attack took place.

"Kill who? What are they talking about?" Yousry asked recently as he sat alongside his wife, Sarah, an evangelical Christian, in their modest Connecticut condominium. "The words I'm looking for, it's insane."

The prosecution and conviction of Stewart, 66, on charges of aiding terrorist activity, drew international attention, overshadowing Yousry's case. But legal experts, civil liberties lawyers and a juror say Yousry's conviction raises many troubling questions, not least how a court-appointed translator working on instruction from lawyers could be held responsible for navigating complicated and dangerous legal waters.

The trial transcripts reveal that prosecutors advanced no evidence to back up certain claims, including the assertion that Yousry was in touch with Middle Eastern terrorists.

"You would expect a translator to take his lead from the defense lawyer and you would not expect that translator to understand the intricacies of a very broad criminal statute," said Neal R. Sonnett, a former federal prosecutor who chaired an American Bar Association task force that opposed the Bush administration's position on enemy combatants. "There is a real issue whether it's even fair to charge, much less convict, someone like him."

Yousry had no legal training and translated nothing without instruction from defense lawyers. He passed rigorous federal security clearance checks. A PhD candidate at New York University, Yousry harbored no affinity for Rahman, writing that the cleric promoted "Muslim totalitarianism."

Justice Department prosecutors said secret recordings of meetings in Rahman's prison showed that Yousry crossed the line between legal and illegal behavior. Yousry read letters to Rahman from radical supporters, even though he understood that they were violent men.

"He stuck his head in the sand and deliberately avoided knowing what would have been obvious," prosecutor Robin Baker told the jury. "We don't need to prove why."